Abstract: A pot experiment was conducted to study the effects of shading on the photosynthetic parameters of Bidens pilosa. The results showed that shading increased the content of chlorophyll a+b, but had less effect on the ratio of chlorophyll a/b. Under high light, the maximum net photosynthetic rate and saturation irradiance of B. pilosa were 3.79 times and 2.71 times of those under shading, respectively. The initial slope of light-response curve of B.pilosa was larger under shading than under high light, while the apparent quantum yield was in adverse. The net photosynthetic rate of B. pilosa under shading was higher than that under high light when the irradiance was below 100 μmol·m^-2·s^-1, and decreased with increasing irradiance when the irradiance was above 650 μmol·m^-2·s^-1. Under high light, the net photosynthetic rate decreased with increasing irradiance only when the irradiance was about 1780 μmol·m^-2·s^-1. It was suggested that shading was an important limiting factor for the growth of B. pilosa.

Key words: Spinacia oleracea, Nitrogen supply, Nitrate, Vitamin C, Oxalate, Antioxidative enzyme activities, Proline